Iron removal

ABSTRACT

A PROCESS FOR SIMULTANEOUSLY DESALTING A HYDOCARBON FEEDSTOCK AND REMOVING IRON PRESENT IN THE HYDOCARBON FEEDSTOCK AS A SOLUBLE ORGANOMETALLIC COMPOUND WHICH COMPRISES CONTACTING THE FEEDSTOCK WITH AN AQUEOUS SOLUTION CONTAINING CYANIDE ION AND THEN SEPARATING AN AQUEOUS BRINE PHASE FROM THE HYDROCARBON FEEDSTOCK. PREFERABLY, THE AQUEOUS SOLUTION CONTAINS IN ADDITION TO CYANIDE ION A REDUCING AGENT SUCH AS AMMONIUM SULFIDE AND PREFERABLY THE FEED IS A CRUDE OIL OR A RESIDUUM FRACTION.

United States Patent U.S. Cl. 208-251 9 Claims ABSTRACT OF THE DISCLOSURE A process for simultaneously desalting a hydrocarbon feedstock and removing iron present in the hydrocarbon feedstock as a soluble organometallic compound which comprises contacting the feedstock with an aqueous solution containing cyanide ion and then separating an aqueous brine phase from the hydrocarbon feedstock. Preferably, the aqueous solution contains in addition to cyanide ion a reducing agent such as ammonium sulfide and preferably the feed is a crude oil or a residuum fraction.

CROSS REFERENCES This application is a continuation in-part of application Ser. No. 766,650, filed Oct. 10, 1968, now Pat. No. 3,562,151 titled Demetalation With Cyanide Ion, which application is incorporated by reference into the present application.

BACKGROUND OF THE INVENTION The present invention relates to a process for removing from hydrocarbon feedstocks metals present as soluble organometallic compounds in the hydrocarbon feedstocks. More particularly, the present invention relates to the removal of soluble iron compounds in combination with desalting of a hydrocarbon feedstock containing both organometallic iron and salt compounds such as sodium chloride, calcium chloride and magnesium chloride.

The presence of metal contaminants in crude oil and fractions thereof is undesirable. Particularly objectionable is the presence of iron in the form of soluble organometallic compounds such as is present frequently to a relatively high parts per million level in Western United States crude oils and residuum fractions. Even when the concentration of iron porphyrin complexes and other iron organometallic complexes is relatively small, i.e., on the order of p.p.m., their presence causes serious difficulties in the refining and utilization of heavy petroleum oils. The presence of an appreciable quantity of the organometallic iron compounds in catalytic cracking feedstocks causes rapid deterioration of the cracking catalysts and changes the selectivity of the cracking catalysts in the direction of more of the charge stock being converted to coke. Also, the presence of an appreciable quantity of the organo-iron compounds in hydroconversion (such as hydrotreating or hydrocracking) feedstocks causes harmful eflfects in the hydroconversion processes such as deactivation of the hydroconversion catalyst and in many instances, plugging or increasing of the pressure drop in fixed bed hydroconversion processes due to the deposition of iron compounds in the interstices between catalyst particles in the fixed bed of catalyst in the hydroconversion reactor.

The iron is held tenaciously in the organometallic compounds so that it is not easy to remove the iron from the oil. In order to obtain substantially complete iron removal, it is necessary to contact the oil with hydrotreating catalyst particles but this process is usually relatively 3,684,700 Patented Aug. 15, 1972 expensive because the catalyst itself is expensive, and the catalyst very rapidly becomes plugged with the iron compounds as they deposit out on the surface of the catalyst. We have found that some of the organo-iron compounds do not hold the iron quite as tenaciously as other of the organo-iron compounds and that a large measure of the iron present in hydrocarbon feedstocks can very advantageously be removed in accordance with the process of the present invention in combination with desalting using an aqueous solution containing cyanide ion.

It was known prior to the present invention that various solvents and other means could be used for the removal of metal contaminants from petroleum oils. For example, Pat. No. 2,472,723 discloses that the detrimental effects of metal, metal oxide and metal-salt contaminants in feedstocks to fluid-catalyst cracking processes are substantially eliminated by continuously contacting the feedstock with a small quantity of contact clay such as that used in lubeoil contacting operations but having a substantially smaller particle size. Pat. No. 2,847,354 discloses a process of upgrading a petroleum oil boiling within the range of from about 450 F. to about 1300 F. and which contains metal-comprising contaminants, said method comprising contacting such an oil with about 50 to 400 volume percent of either hydantoin or an alkyl-substituted hydantoin at a temperature within the range of from about F. to about 500 F., and segregating a treated oil. Pat. No. 2,870,081 discloses a process of removing metal-containing contaminants from an oil which comprises subjecting such an oil to a direct voltage electrical field of at least 15,000 volts per centimeter for a time sufiicient to remove such contaminants from the said oil. Pat. No. 2,911,355 discloses an improved fractionation method for elfectively separating metal contaminants from gas oils. Pat. No. 2,913,394 discloses the use of butyrolactone in removing metal contaminants from a hydrocarbon oil boiling within the range of from about 450 F. to about 1300 F.

US. Pat. 2,703,306 is directed to a process for removing iron using a reagent selected from the group consisting of ammonium oxylate and ammonium thiocyanate. The process of U. S. Pat. 2,703,306 is directed to contacting iron contaminated mineral oils so as to remove a substantial amount of the iron using ammonium compounds. The ammonium oxylate and ammonium thiocyanate in the aqueous contacting solution are present to a substantial extent in the ionized form, NH C 0,: for the ammonium oxylate, and NH NCS" for the ammonium thiocyanate. For the ammonium thiocyanate, there is substantially no free cyanide because thiocyanate is stable and does not decompose to cyanide and sulfur.

As indicated previously, the present invention relates to the combined desalting and removal of iron compounds from hydrocarbon feedstocks. The removal of salty compounds such as sodium, calcium, and magnesium chloride from crude oils has, of course, been carried out for many years. The literature describes numerous desalting processes. Among the most important are electrical precipitation, simple washing and settling, heat and pressure processes, chemical treatment processes, solid contacting processes, and centrifuging.

The present invention is utilized in combination only with those desalting techniques involving water contacting of the hydrocarbon feedstock. A large number of the Various desalting techniques falling in the various categories as mentioned above use a water contacting step because of the high solubility of the salty materials in water.

Electrical desalting processes usually depend upon the following two steps:

(1) Emulsification of the salty crude oil with added water, where the oil or water, or both, are preheated usually to 140 to 190 F. The quantity of added wash water ranges from to 50 percent by volume of the oil to be washed.

(2) The crude oil and water emulsion is kept at a temperature of 130 to 300 F., and the water and salt are separated by an electric field contained in a vessel that is maintained at a pressure, usually of to 70 pounds per square inch.

The removal of salt from crude oil by simply washing the oil with water at atmospheirc temperatures and then allowing the two liquids to separate by natural gravitational settling has proved satisfactory only in those cases where the original crude oil does not tend to form a stable emulsion and is a comparatively light oil with a low viscosity. At best, this process, without modification, gives a low salt-removal efiiciency, but fundamentally most of the present commonly used processes are based on this method, with modifications to improve efiiciency.

Various desalting techniques are discussed in Bulletin RI3422 of the Bureau of Mines titled Desalting Crude Petroleum, which bulletin is incorporated by reference into the present patent application.

SUMMARY OF THE INVENTION According to the present invention, a process is provided for simultaneously desalting a hydrocarbon feedstock and removing iron present in the hydrocarbon feedstock as a soluble organometallic compound which comprises contacting the feedstock with an aqueous solution containing cyanide ion and then separating an aqueous brine phase from the hydrocarbon feedstock.

A wide variety of hydrocarbon feedstocks can be processed in the present invention. As indicated in the parent application, Ser. No. 766,650, it has been found that the cyanide contacting is particularly advantageously used to remove iron compounds from hydrocarbon feedstocks selected from the group consisting of crude oils, deasphalted oils, shale oils, residua and topped crude oils. The term crude oils in Ser. No. 766,650 includes whole crudes, such as are obtained directly from oil wells, and other crude oils such as vacuum gas oils and heavy vacuum gas oils which have not been subjected to solvent treatment or catalytic treatment such as hydrotreating. The present invention, which is a combined process for desalting and iron removal, is most advantageously applied to whole crude oils before the whole crude oil is subjected to atmospheric distillation, the atmospheric distillation step being the basic distillation step of a refinery to split the whole crude oil up into various feedstocks for further treatment.

The process of the present invention is also advantageously applied to the desalting of residuum and the removal of iron from residuum feedstocks. The term residuum is used herein to mean reduced crudes obtained from the bottom of atmospheric distillation units and vacuum residuums obtained from; the bottom of vacuum distillation columns. Residuum fractions of crude oils are usually not desalted in addition to the desalting of the crude oil when the crude oil is desalted in the same refinery in which the residuum feedstock is to be processed. However, in certain instances, residuum feedstocks are transferred from one refinery to another making desalting of the residuum fraction desirable because the residuum generally becomes contaminated again with brine present in the shipping taniks, particularly the shipping storage facilities of ships or seagoing vessels used to transport the residuum from one location to another.

In general, the process of the present invention is preferably applied to heavy oil hydrocarbon feedstocks including those specifically mentioned above. The heavy oil feedstocks usually are those at least weight percent of which boil above 650 F. The heavy oil feedstocks contain a relatively large amount of organo-iron compounds com,- pared to lighter oils.

In carrying out the process of the present invention, at

least 20 p.p.m. cyanide ion is preferably present in the aqueous solution used for treating the heavy oil hydrocarbon feedstock and more preferably, at least 50 p.p.m. cyanide ion by weight is present in the aqueous solution used for the simultaneous desalting and iron removal.

One of the important advantages of the process of the present invention is that the process of the present invention does not rely on a filtration step but instead, operates to remove the iron from the organic feedstock by complexing or otherwise causing the iron to become soluble in the aqueous phase present while simultaneously effecting desalting of the hydrocarbon feedstock. Treating feedstocks containing organo-iron compounds with ammonium compounds, particularly ammpnium sulfide, was found to result in the precipitation of iron compounds, thus necessitating a filtering or other physical separating step to remove precipitated iron. However, the use of cyanide containing aqueous solution in accordance with the process of the present invention is effective for the removal of at least one-third of the iron present in the hydrocarbon feedstock and usually 40-50 percent or more without employing any filtration step.

Preferably, the aqueous solution used for desalting and removing iron from the hydrocarbon feedstock contains a reducing agent in addition to cyanide ion. We have found that using a reducing agent in addition to the cyanide ion results in lower iron contents for the treated oil than when only the cyanide ion is used. Suitable reducing agents include agents effective to reduce ferric ion to the ferrous state. Included in the suitable reducing agents are hydrazine, ammonium sulfite, ammonium sulfide and other reducing agents disclosed, for example, in US. Pat. 3,459,658, which patent is incorporated by reference into the present specification. Ammonium sulfide is a particularly preferred reducing agent. Preferably, the cyanide ion is present in concentrations between about 2-5 percent and the reducing agent is present in an amount of about 10 p.p.m. up to about 2-5 weight percent.

According to a particularly preferred embodiment of the present invention, the aqueous solution which is used to carry out the simultaneous desalting and iron removal is a foul water solution obtained from a catalytic cracking unit. The term catalytic cracking is used in this connection to refer to cracking processes carried out at high temperatures, usually between about 900 and 1200 F. in the presence of catalyst particles such as silica-alumina with or without added crystalline zeolitic components. The two major types of catalytic cracking processes are fluid catalytic cracking and moving bed catalytic cracking. In the typical catalytic cracking units, products from the cracking reactor are fractionated and overhead material from the fractionation zone typically includes a foul water stream containing some cyanide ion in addition to other components including ammonia and sulfide ion. As previously indicated, the process of the present invention is preferably carried out using an aqueous solution containing ammonium sulfide in addition to cyanide ion; thus, the catalytic cracking unit foul water contains at least two constituents in addition to water which are particularly important for a preferred aqueous solution used in the process of the present invention. Also, in most refineries, catalytic cracking is carried out to upgrade portions of the crude oil into more valuable products. Thus, it is economically advantageous to be able to utilize the foul water generated in the catalytic cracking process in combination with the process used to desalt and remove iron from heavy oil which eventually is fed at least in part to the catalytic cracking unit.

We have found that temperatures above about F. and more preferably, above about F. are preferable in the contacting step of the process of the present invention for removing iron. Temperatures between about 100 and 350 F., particularly between about 180 and 300 F., are preferred both from the standpoint of eflicient desalting and efficient iron removal from the hydrocarbon feedstock.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating a preferred overall process embodiment for the process of the present invention.

DETAILED DESCRIPTION Referring now more particularly to the drawing, a hydrocarbon feed is introduced to exchanger 2 via line 1 wherein the hydrocarbon feed is heated, for example by exchange with a hot hydrocarbon stream from the atmospheric distillation column in the refinery. Preferred heavy oil hydrocarbon feedstocks are crude oils and residuum fractions as discussed previously. The heavy oil feedstock is withdrawn from exchanger 2 via line 3 preferably at a temperature of about l90 250 F. and is fed together with Water recycled via line 6 to desalter 7 via line 4.

Various types of desalter processes and apparatuses can be used in the process of the present invention with the most important feature being good contact of the aqueous solution with the heavy oil and adequate residence time for both the desalting and iron removal reactions or steps to occur. Residence time in the contacting and/or settling vessel preferably is at least minutes and more preferably is 20 minutes or more.

The aqueous cyanide solution is introduced to the process as indicated in the schematic process flow diagram via lines 8 or 8A. The cyanide ion solution is introduced to the desalter via lines 9 and 10 in addition to the aqueous cyanide solution which is recycled via line 6. The schematic flow path indicated for desalter 7 represents a countercurrent flow path for at least a portion of the heavy oil feedstock and the aqueous cyanide solution in desalter 7. Various arrangements may be utilized for effecting the contacting of the heavy oil with the aqueous cyanide solution including processes employing electrical precipitation or centrifugation or etc. to aid in the simultaneous desalting of the heavy oil feedstock while the heavy oil feedstock is also being treated for iron removal.

The desalted heavy oil is removed from the desalting and iron removal contacting step via line 12 and is passed to distillation facilities in zone 13. The distillation facilities in the case of whole crude typically comprise an atmospheric distillation column operated at pressures usually between about atmospheric and 40 p.s.i.g. and frequently also a vacuum distillation column operated at a pressure of about 1 or 2 p.s.i.a. to remove vacuum gas oil fractions from the reduced crude obtained from the bottom of the atmospheric distillation column.

The process of the present invention is preferably employed in combination with catalytic cracking as indicated schematically by zone 14 and also the process of the present invention is advantageously used in combination with hydroconversion processes, particularly fixed bed hydroconversion processes such as fixed bed hydrotreating and hydrocracking.

In fixed bed hydrotreating or hydrocracking, iron frequently deposits in the interstices between the catalyst particles in the fixed beds causing increasing pressure drops in the fixed catalyst beds. The removal of a large amount of the iron in the hydrocarbon feedstock reduces the rate of pressure drop buildup across the fixed catalyst beds used in hydroconversion processes wherein iron deposits out due to the hydrogenation and hydrocracking reactions in which organo-iron compounds become involved. Hydrotreating processes also are, of course, advantageously used in combination with catalytic cracking to provide feedstocks which are more readily converted to gasoline and other valuable products by catalytic cracking. Thus, according to the process flow diagram, a portion of the oil as, for example, an organic sulfur and organic nitrogen contaminated portion is removed via line 16 from distillation zone 13 and is passed to hydroconversion zone 15. After hydrotreating the sulfur and nitrogen contaminated oil in hydroconversion zone 15, a portion of the hydroconverted hydrocarbon may be withdrawn as a gasoline or jet fuel product via line 17 and another portion withdrawn via line 18 and fed to catalytic cracking zone 14. The feedstock via line 18 to catalytic cracking zone 14 is particularly suitable for catalytic cracking in that it has reduced sulfur and nitrogen content as well as reduced iron and other metals content. Another portion of the heavy oil feed to distillation zone 13 is withdrawn from the distillation zone via line 19 and fed to catalytic cracking zone 14. Product gasoline or other valuable hydrocarbons are withdrawn from zone 14 via line 20.

Foul water containing cyanide ion is Withdrawn from catalytic cracking zone 14 via line 8A for use in the combined desalting-iron removal process in accordance.

with a preferred embodiment of the present invention. The catalytic cracking zone 14 may comprise, for example, a fluid catalytic cracking plant including reactor and fractionation sections. Various fluidized catalytic cracking processes carried out at temperatures of about 900 or 1000" F. and pressures of about 5 to 20 p.s.i.g. are well-known in the art. The cracked vaporized hydrocarbons from the reactor are introduced to fractionation facilities as, for example, a large main fractionator frequently operated in conjunction with sidecut stripping columns from which are obtained stripped sidedraws from the main fractionator such as light cycle oil and medium cycle oil. The overhead from the main fractionator may be withdrawn at a temperature between about 200 and 300 F. The overhead from the fractionator is condensed and introduced at a temperature of about F. and a pressure of about 9 p.s.i.g. into an overhead receiving vessel, a gaseous hydrocarbon stream is withdrawn from the top of the overhead vessel and a liquid hydrocarbon stream containing ethane up to about 0 C or C hydrocarbons is withdrawn as a liquid from the overhead receiving vessel for the main fractionator. A foul water or sour water stream containing cyanide ion is withdrawn as a liquid from a lower part or a leg in the overhead receiving vessel. This foul water stream as indicated previously is preferably used in the desalting-iron removal step in accordance with the present invention as is indicated by line 8A from catalytic cracking zone 14.

EXAMPLES 1) The data in the following Table I illustrate iron removal in accordance with the process of the present invention. In the runs illustrated in this table, iron-contaminated, deasphalted oils were contacted with various types of aqueous cyanide solutions under different conditions of temperature and pressure. Iron contents of the feed oils varied from 6 to 24 ppm. iron. Nickel and vanadium were present in amounts from 10 to 50 and 4 to 21 ppm, respectively.

TABLE I Run A B C D E F Treating agent:

yn ImtIaI CN-content, p.p.m 162 162. 000 600 162 162 Added CN,p.p.m 0 0 0 0 540 500 Total CN-c0ntent, p.p.m 162 162 1, 000 2, 600 702 662 Volumetric analysis:

Oil, cc 150 35 150 170 Xylene diluent, 00...- 300 345 265 300 340 Treating agent, cc 150 300 300 150 305 Treating conditions:

Temperature, F-.. 90 167 400 149 196 Pressure, p.s.i.g 0 0 0 2, 300 0 0 Contracting time, nu 15 15 16 30 5 15 Metals removal, percent:

Iron 62 86 86 67 91 96 Nickel 6 1 1 12 1 1 Vanadium 1 1 1 9 1 1 1 Foul water. 9 NaCN solution.

3 NaGN solution, also contains hydrogen dissolved in solution.

It willbe apparent from the above table that over a wide range of contacting temperatures and pressures and with varying amounts of cyanide ion and varying ratios of volumes of treating agent per volume of oil, there was a high degree of removal of iron from the contaminated oil, although at the same time essentially no removal of nickel and vanadium until the cyanide ion concentration became extremely high. This property of selective iron removal is especially useful in instances where a particular oil as an iron content disproportionately high compared to its content of other metals, so that iron removal will constitute the major part of any demetalation process.

(2) Calculated salt removal, i.e., removal of sodium chloride, calcium chloride and magnesium chloride, using the same contacting conditions including a temperature of about 167 F., a pressure of about p.s.i.g. and a contacting time of about 15 minutes as in Run B in Table I above, is about 85 percent.

(3) A residuum feedstock having an API gravity of about 6.3 and a boiling range of about 750 F. to 1200 F. and a metals content of about 81 p.p.m. iron calculated as iron but present as organo-iron compounds, was treated with an aqueous solution containing 5 weight percent ammonium sulfide at a temperature of 197 F. for minutes. The resulting iron content for the recovered hydrocarbon was 66 p.p.m. for an iron removal of less than percent. In treating another heavy oil, in particular, a solvent deasphalted oil, the iron was reduced from 24 p.p.m. iron to 7 p.p.m. iron for a 71 percent iron removal by using an aqueous solution containing sodium cyanide. The contacting time used in the sodium cyanide treatment of the solvent deasphalted oil was the same as that used when only 20 percent iron removal was obtained using ammonium sulfide on residuum and the temperature was also about the same (199 F. vs. 197 F.).

Still further improved results were obtained by carrying out the contacting of the solvent deasphalted oil using ammonium sulfide as a reducing agent in addition to the cyanide ion present in the aqueous contacting solution. The iron content of the solvent deasphalted oil was reduced from 24 p.p.m. iron to 1 p.p.m. iron for a 96 percent iron removal. Certain heavy oil feedstocks contain more iron which is extremely difiicult to remove and thus, iron removal efiiciencies as high as 96 percent cannot consistently be expected. In any case, the combined ammonium sulfide reducing agent plus sodium cyanide results in highly efiective iron removal which is far superior to that obtained using simply ammonium sulfide and also apparently somewhat superior to the iron removal obtained using only cyanide ion.

Using the combination sodium cyanide-ammonium sulfide treatment for the residuum having an API gravity of 6.3 and boiling range of 750 F. to 1200 F., the iron was reduced from 81 p.p.m. to 19 p.p.m. Thus, the percent iron removal was about 77 percent compared to only about 20 percent when only the 5 weight percent ammonium sulfide was used. However, this latter result is only directional data showing the superiority of sodium cyanide used together with ammonium sulfide as opposed to using only ammonium sulfide because the contacting temperature and the contacting time were higher in the case of this combination treatment (600 F., 2 hours contacting time). The higher temperature and greater contacting time are believed clearly not to be solely responsible for the large ditference in the percent iron removed, especially in view 6 of the data as tabulated in Table I illustrating a relatively weak dependence of iron removal efliciency on contacting temperature and time so long as the contacting temperature is above about F. and the contacting time above about 15 minutes.

Although various embodiments of the invention have been described, it is to be understood that they are meant to be illustrative only and not limiting. Certain features may be changed without departing from the spirit or scope of the present invention. It is apparent that the present invention has broad application to the simultaneous desalting and removal of iron from hydrocarbons using an aqueous solution containing cyanide ion. Accordingly, the invention is not to be construed as limited to the specific embodiments or examples discussed but only as defined in the appended claims.

We claim:

1. A process for simultaneously desalting a hydrocarbon feedstock and removing iron present in the hydrocarbon feedstock as a soluble organometallic compound which comprises contacting the feedstock with an aqueous solution containing cyanide ion and then separating an aqueous brine phase from the hydrocarbon feedstock.

2. A process in accordance with claim 1 wherein the hydrocarbon feedstock is a heavy oil at least 25 weight percent of which boils above 650 F.

3. A process in accordance with claim 1 wherein the hydrocarbon feedstock is a crude oil or a residuum fraction.

4. A process in accordance with claim 1 wherein the aqueous solution contains at least 50 p.p.m. of cyanide 1011.

5. A process in accordance with claim 1 wherein the aqueous solution contains a reducing agent and cyanide ion.

6. A process in accordance with claim 5 wherein the reducing agent is ammonium sulfide.

7. A process in accordance with claim 1 wherein the aqueous solution is a foul water stream from a catalytic cracking process with the foul water stream containing at least 50 p.p.m. cyanide ion.

8. A process in accordance with claim 1 wherein the contacting of the hydrocarbon feedstock with the aqueous solution is carried out at a temperature between 100 and 350 F.

9. A process for simultaneously desalting and removing iron from a feedstock selected from the group consisting of crude oil and residuum which comprises contacting the feedstock at a temperature between 100 and 350 F. with an aqueous solution containing at least 50 p.p.m. cyanide ion and then separating an aqueous phase containing dissolved salts and iron complexes and recovering desalted and deironed hydrocarbon feedstock.

References Cited UNITED STATES PATENTS 3,562,151 2/1971 Langlois et al. 208251 2,703,306 3/ 1955 Asselin 20825 1 3,252,891 5/1966 Gleim 208--206 2,235,936 3/1941 Lerch et al. 19630 2,069,329 2/ 1937 Roelfsema 208236 3,205,164 9/1965 Brown 208207 2,216,856 10/1940 Short 19690 2,723,944 11/1955 Chenicek 208207 2,028,998 1/1936 Schulze et al 208207 2,701,783 2/1955 Long et al 19614.12

5 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner US. Cl. X.R. 208289 

